Minimally invasive implantable neurostimulation system

ABSTRACT

A neuromodulation therapy is delivered via at least one electrode implanted subcutaneously and superficially to a fascia layer superficial to a nerve of a patient. In one example, an implantable medical device is deployed along a superficial surface of a deep fascia tissue layer superficial to a nerve of a patient. Electrical stimulation energy is delivered to the nerve through the deep fascia tissue layer via implantable medical device electrodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 61/734,425, filed Dec. 7, 2012 (Atty. DocketC00003998.USP1), which application is incorporated herein by referenceas if re-written in its entirety.

The present application claims priority to U.S. Provisional PatentApplication No. 61/777,804, filed Mar. 12, 2013 (Atty. DocketC00003998.USP3), which application is incorporated herein by referenceas if re-written in its entirety.

The present application claims priority to U.S. Provisional PatentApplication

No. 61/734,429, filed Dec. 7, 2012 (Atty. Docket C00004420.USP1), whichapplication is incorporated herein by reference as if re-written in itsentirety.

The present application claims priority to U.S. Provisional PatentApplication No. 61/777,949, filed Mar. 12, 2013 (Atty. DocketC00004420.USP3), which application is incorporated herein by referenceas if re-written in its entirety.

The present application claims priority to U.S. Provisional PatentApplication No. 61/734,446, filed Dec. 7, 2012 (Atty. DocketC00004588.USP1), which application is incorporated herein by referenceas if re-written in its entirety.

The present application claims priority to U.S. Provisional PatentApplication No. 61/777,824, filed Mar. 12, 2013 (Atty. DocketC00004588.USP2), which application is incorporated herein by referenceas if re-written in its entirety.

The present application claims priority to U.S. Provisional PatentApplication No. 61/777,838, filed Mar. 12, 2013 (Atty. DocketC00004588.USP5), which application is incorporated herein by referenceas if re-written in its entirety.

The present application claims priority to U.S. Provisional PatentApplication No. 61/734,436, filed Dec. 7, 2012 (Atty. DocketP40339.USP1), which application is incorporated herein by reference asif re-written in its entirety.

The present application claims priority to U.S. Provisional PatentApplication No. 61/777,787, filed Mar. 12, 2013 (Atty. DocketP0040339.USP3), which application is incorporated herein by reference asif re-written in its entirety.

FIELD OF THE DISCLOSURE

The disclosure relates generally to implantable neurostimulation systemsand in particular to minimally invasive neurostimulation systems.

SUMMARY

Various exemplary embodiments of a minimally invasive implantablemedical device system deliver neurostimulation to a targeted nerve orneural tissue through a tissue layer. In one embodiment, a method forproviding neuromodulation includes deploying an implantable medicaldevice along a superficial surface of a deep fascia tissue layersuperficial to a nerve of a patient and delivering electricalstimulation energy via electrodes coupled to the device to stimulate thenerve through the deep fascia tissue layer. In one example the nerve isthe tibial nerve and the device is implanted along a superficial surfaceof a deep fascia tissue layer extending over the tibial nerve. Deployingthe device may include dissecting a tissue pocket using a first end of adissection tool and delivering test stimulation pulses using anelectrode coupled to the first end of the dissection tool andelectrically coupled to a pulse generator via a connecter at a secondend of the dissection tool to locate the tibial nerve. A second end ofthe dissection tool may include an incising blade for making a skinincision.

Deploying the implantable medical device may include positioning atleast one electrode carried along a face of a housing of the implantablemedical device against the tissue layer and/or advancing an electricallead, carrying at least one electrode, along the tissue layersuperficial to the tibial nerve. The method for providing theneuromodulation therapy may further include providing power from anexternal device positioned cutaneously over the implantable medicaldevice for powering the generation of stimulation pulses delivered tothe nerve via the plurality of electrodes.

Deploying the implantable medical device may further include fixatingthe implantable medical device along the tissue layer using a fixationmember. A passive fixation member extending from a housing of theimplantable medical device may be engaged in a surrounding tissue. Inother examples, fixating the implantable medical device includesinserting an active fixation member into the tissue layer to capture thetissue layer between a housing of the implantable medical device and aportion of the active fixation member. Inserting an active fixationmember into the tissue layer may include advancing the active fixationmember through an aperture of a housing of the implantable medicaldevice.

In one embodiment, a system for delivering a neuromodulation therapyincludes an implantable medical device configured to be deployed along asuperficial surface of a deep fascia tissue layer superficial to a nerveof a patient. The implantable medical device includes a housing,electrodes and a pulse generating circuit enclosed in the housing fordelivering electrical stimulation pulses via the electrodes to the nervethrough the deep fascia tissue layer. The system may further include adissection tool having a first end for dissecting a tissue pocket and asecond end comprising an electrical connector. The dissection tool mayinclude an electrode coupled to the first end and electrically coupledto the connector; the connector adapted to be coupled to a pulsegenerator for delivering test stimulation pulses via the electrodecoupled to the dissection tool to locate the nerve. The second end ofthe dissection tool may include an incising blade for making a skinincision.

In various embodiments, the implantable medical device system includesat least one electrode carried along a face of the housing of theimplantable medical device configured to be positioned against thesuperficial surface of the tissue layer. Additionally or alternatively,the implantable medical device includes an electrical lead carrying atleast one electrode adapted to be advanced along the superficial surfaceof the tissue layer. The system may include an external device fortransmitting power from a cutaneous position over the implantablemedical device for powering the pulse generator to generate stimulationpulses delivered to the nerve via the electrodes.

The system may further include a fixation member for fixating theimplantable medical device along the superficial surface of the tissuelayer. The fixation member may include a passive fixation memberextending from a housing of the implantable medical device for engaginga surrounding tissue. Additionally or alternatively, the system of claimmay include an active fixation member adapted to be inserted into thetissue layer for fixating the implantable medical device by capturingthe tissue layer between the housing of the implantable medical deviceand a portion of the active fixation member. The housing may include anaperture for receiving the active fixation member, the active fixationmember configured to be advanced through the aperture into the tissuelayer.

In one exemplary embodiment, a method for delivering a neurostimulationtherapy includes delivering electrical stimulation energy via at leastone electrode positioned subcutaneously and superficially to a deepfascia tissue layer superficial to a tibial nerve to stimulate thetibial nerve through the deep fascia tissue layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of an exemplary minimally invasive IMDsystem capable of delivering a neurostimulation therapy.

FIGS. 1B-1F are schematic illustrations depicting exemplary implantlocations of an exemplary IMD system for delivering a neurostimulationtherapy relative to a patient's anatomy.

FIG. 2 is a functional block diagram of the IMD shown in FIG. 1Aaccording to one exemplary embodiment.

FIG. 3 is a perspective view of an exemplary IMD that may be included inan INS system according to one embodiment.

FIG. 4 is a perspective view of the IMD shown in FIG. 3 after exemplarypuncture tips are removed.

FIG. 5 is a perspective view of an exemplary fixation shroud accordingto an illustrative embodiment.

FIG. 6 is a perspective view of an exemplary implantation tool adaptedfor use with the IMD shown in FIG. 3.

FIG. 7 is a perspective view of the implantation tool of FIG. 6 afterremoving IMD from a retaining sleeve.

FIG. 8 is a side plan view of the implantation tool and the IMD shown inFIG. 6 after being deploying to desired implant site.

FIG. 9 is a perspective view of an exemplary IMD having active fixationmembers.

FIG. 10 is a perspective view of the IMD shown in FIG. 9 after deployingfixation members.

FIG. 11 is a perspective view of an exemplary IMD including shape memoryfixation members according to an alternative embodiment.

FIG. 12 is a perspective view of the IMD of FIG. 11 with the fixationmembers in a deployed position.

FIG. 13 is an exemplary IMD including a fixation member according to analternative embodiment.

FIG. 14 is a perspective view of an exemplary implantation tool for usein implanting the IMD shown in FIG. 13.

FIG. 15 is a perspective view of an exemplary IMD and plunger of theimplantation tool shown in FIG. 14.

FIG. 16 is a close-up bottom perspective view of the plunger shown inFIG. 15.

FIG. 17 is perspective view of the plunger of FIG. 15 from a differentangle.

FIG. 18 is a side view of an exemplary fixation structure loaded in thehollow needle of the implant tool shown in FIG. 14 according to analternative embodiment.

FIG. 19 is a side view of an exemplary IMD fixed at a desired implantlocation using the fixation structure shown in FIG. 18.

FIG. 20 is a close-up perspective view of an alternative exemplaryembodiment of a fixation member loaded in a hollow needle.

FIG. 21 is a perspective view of the fixation member shown in FIG. 20deployed for anchoring an IMD against a tissue layer.

FIG. 22 is a perspective view of an alternative exemplary embodiment ofan IMD fixation member.

FIG. 23 is a perspective view of an exemplary fixation member anchoringan IMD against a tissue layer.

FIG. 24 is a perspective view of the fixation member shown in FIG. 22including a compliant grommet.

FIG. 25 is a perspective view of an alternative exemplary fixationmember including a “U” shaped clip.

FIG. 26 is a plan view of an exemplary IMD including a housing enclosinginternal IMD circuitry and a lead tethered to the housing via anelectrically insulated, sealed feedthrough.

FIG. 27A is a perspective view of an exemplary IMD including a housingand a receptacle for receiving a connector of a lead.

FIG. 27B is a perspective view of an alternative exemplary embodiment ofan IMD having a tethered lead.

FIG. 28 is a perspective view of an exemplary IMD including a housingtethered to an elongated lead adaptor at an electrically insulatedsealed electrical feed through.

FIGS. 29A and 29B are perspective views of an exemplary implant tool andthe IMD shown in FIG. 26.

FIG. 30 is a perspective view of the IMD and lead of FIG. 26 after beingdeployed to an implant site using the implant tool of FIG. 29A.

FIG. 31 is a perspective view of another exemplary embodiment of animplant tool that may be used to deploy an IMD and lead to a desiredimplant location in a minimally invasive procedure.

FIG. 32 is an enlarged perspective view of a distal portion of theimplant tool of FIG. 31.

FIGS. 33 a-33 d show perspective views of an exemplary implant toolbeing used to deploy an IMD and lead to a desired implant site.

FIGS. 34 and 35 are perspective views of an alternative exemplaryembodiment of an IMD and lead including distal fixation members andproximal fixation members.

FIG. 36 is a side view of an exemplary IMD including a fixation memberconfigured as a curved barb or hook.

FIG. 37 is a side view of the IMD shown in FIG. 36 after fixationagainst a tissue layer.

FIG. 38 is a side view of an alternative exemplary embodiment of an IMDincluding a fixation member hook.

FIG. 39A is a side view of an exemplary IMD including one or moreelectrodes embodied as feedthrough pins extending from IMD housing.

FIG. 39B is a perspective view of an exemplary feedthrough assembly.

FIG. 40 is an enlarged perspective view of an exemplary feedthrough pin.

FIG. 41 is a depiction of a variety of exemplary stamped or preformedfeedthrough pins including variously shaped exemplary distal ends

FIG. 42 is a perspective view of an exemplary fixation member electrodeand feedthrough assembly.

FIG. 43 is a bottom perspective view of an IMD including the fixationmember electrode and feedthrough assembly of FIG. 42.

FIG. 44 is a perspective view of an exemplary implant tool for use in aminimally invasive IMD implantation procedure.

FIG. 45 is a perspective view of an alternative exemplary embodiment ofan implant tool.

FIG. 46 is a flow chart of an exemplary method for delivering aneurostimulation therapy.

DETAILED DESCRIPTION

Applicants have an appreciation that implantable medical device (IMD)technology is continually advancing as new applications are developedfor automated therapy delivery in patients. Such advances may be furtherenhanced by using devices of reduced size and weight, which makesimplantation of such devices less invasive and chronic use morecomfortable for the patient. Additionally, applicants recognize thatsuch enhancements such as improved power supply systems, wirelesstelemetry systems for communication with the implanted device, tools forperforming implantation procedures, apparatus and methods for targetinga delivered therapy at a desired location, and other system improvementscan also enhance therapies in a manner that saves cost, conserves energyand minimizes any burden placed on the patient or clinician.Accordingly, Applicants recognize a need for improved,minimally-invasive implantable medical device systems and associatedmethods of use for providing patient monitoring and/or therapy delivery.Certain exemplary embodiments disclosed herein may obtain some or all ofthe aforementioned advantages and enhancements.

When implanting small devices at targeted monitoring or therapy deliverylocations, stable fixation of the device can be important, though notnecessarily essential, in achieving effective therapy delivery and/oraccurate monitoring of physiological signals. Stable fixation at aselected implant site can reduce power requirements of a devicedelivering an electrical stimulation therapy because therapy deliveryelectrodes can be positioned at an optimal location to delivertherapeutic pulses. Accordingly, Applicants recognize a need forimproved, minimally-invasive implantable medical device systems andassociated methods of use for providing stationary and/or ambulatorypatient monitoring and/or therapy delivery.

In the following description, references are made to illustrativeembodiments. Various embodiments of electrodes, fixation mechanisms andimplant delivery tools for an IMD included in an implantableneurostimulation (INS) system for delivering an electrical stimulationtherapy to a targeted neural site are described. However, it isrecognized that the various embodiments described herein may beimplemented in numerous types of IMDs, including, for example,implantable sensors or monitoring devices, implantable communicationdevices, and other types of implantable therapy delivery systems. Thevarious embodiments of IMD systems described herein and associatedmethods of manufacture promote and facilitate minimally invasiveimplantation procedures in which the incision size and time required toimplant and anchor the device can be minimized. The fixation mechanismsprovide stable positioning of the IMD to promote efficient therapydelivery (and/or accurate monitoring in a sensing device).

FIG. 1A is a schematic diagram of a minimally invasive INS system 10capable of delivering a neurostimulation therapy. System 10 includes anIMD 20, an external device 40 enabled for transmitting signals to IMD20, a patient programming device 60 enabled for bidirectionalcommunication with IMD 20 and/or external device 40, and a physicianprogramming device 80 according to an illustrative embodiment. In theillustrative embodiments described herein, communication betweencomponents included in the INS system 10 is configured to bebidirectional communication, however it is recognized that in someembodiments communication between two or more system components may beunidirectional.

IMD 20 includes electronic circuitry, e.g., comprising one or moreelectronic circuits, for delivering neurostimulation pulses enclosed ina sealed housing and coupled to therapy delivery electrodes. In variousembodiments, IMD 20 may include one or more of a primary battery cell, arechargeable battery cell, and an inductively coupled power source forproviding power for generating and delivering stimulation pulses andpowering other device functions such as communication functions.

In some embodiments, IMD 20 is less than approximately 30 mm in length,or less than approximately 15 mm in length, and less than approximately1 cc in volume. In illustrative embodiments, the term “approximately” asused herein may indicate a value of±10% of a stated value or maycorrespond to a range of manufacturing specification tolerances. Inother examples, IMD 20 may be less than approximately 10 mm in lengthand may be less than approximately 0.6 cc in volume. IMD 20 may beapproximately 0.1 cc in volume in some embodiments. The embodimentsdescribed herein are not limited to a particular size and volume of IMD20, but are generally implemented to enable the use of a reduced sizedevice for minimally invasive implantation procedures and minimizeddiscomfort to a patient. It is recognized, however, that the various IMDsystems described herein may be implemented in conjunction with a widevariety of IMD sizes and volumes adapted for a particular therapy ormonitoring application.

External device 40 may be a wearable device including a strap 42 orother attachment member(s) for securing external device 40 to thepatient in operable proximity to IMD 20. When IMD 20 is provided withrechargeable battery cell(s), external device 40 may be embodied as arecharging unit for transmitting power, for example inductive powertransmission from external device 40 to IMD 20. In this embodiment,programming device 60 may be a patient handheld device that is used toinitiate and terminate therapy delivered by IMD 20 via a bidirectionalwireless telemetry link 62. Alternatively, programming device 60 couldbe operated by a patient for communicating with wearable external device40 to control therapy on and off times and other therapy controlparameters, which are transmitted to IMD 20 via communication link 21.Programming device 60 may communicate with wearable external device 40via a bidirectional wireless telemetry link 41 that may establishcommunication over a distance of up to a few feet, enabling distancetelemetry such that the patient need not position programming device 60directly over IMD 20 to control therapy on and off times or performother interrogation or programming operations (e.g., programming ofother therapy control parameters).

When IMD 20 includes primary cell(s), a wearable external device 40 maybe optional. Programming of IMD 20 may be performed by the programmingdevice 60, using near- or distance-telemetry technology for establishingbidirectional communication link 62 for transmitting data betweenprogrammer 60 and IMD 20. Programming device 60 may be used by a patientor clinician to set a therapy protocol that is performed automaticallyby IMD 20. Programming device 60 may be used to manually start and stoptherapy, adjust therapy delivery parameters, and collect data from IMD20, e.g. data relating to total accumulated therapy delivery time orother data relating to device operation or measurements taken by IMD 20.

When IMD 20 is configured as an externally powered device, externaldevice 40 may be a power transmission device that is worn by the patientduring a therapy session to provide power needed to generate stimulationpulses. For example, external device 40 may be a battery powered deviceincluding a primary coil used to inductively transmit power to asecondary coil included in IMD 20. External device 40 may include one ormore primary and/or rechargeable cells and therefore may include a poweradaptor and plug for re-charging in a standard 110V or 220V wall outlet,for example.

It is contemplated that in some embodiments the functionality requiredfor transmitting power to IMD 20 when IMD 20 is embodied as arechargeable or externally powered device and for programming the IMD 20for controlling therapy delivery may be implemented in a single externaldevice. For example, power transmission capability of external device 40and programming capabilities of patient programmer 60 may be combined ina single external device, which may be a wearable or handheld device.

Physician programming device 80 may include increased programming anddiagnostic functionality compared to patient programming device 60. Forexample, physician programming device 80 may be configured forprogramming all neurostimulation therapy control parameters, such as butnot limited to pulse amplitude, pulse width, pulse shape, pulsefrequency, duty cycle, therapy on and off times, electrode selection,and electrode polarity assignments. Patient programming device 60 may belimited to turning therapy on and/or off, adjusting a start time oftherapy, and/or adjusting a pulse amplitude without giving access to thepatient to full programming functions such that some programmingfunctions and programmable therapy control parameters cannot be accessedor altered by a patient.

Physician programming device 80 may be configured to communicatedirectly with IMD 20 via wireless, bidirectional telemetry link 81, forexample during an office visit. Additionally or alternatively, physicianprogramming device 80 may be operable as remote programming instrumentused to transmit programming commands to patient programming device 60via a wired or wireless communication network link 61, after whichpatient programming device 60 automatically transmits programming datato IMD 20 via bidirectional telemetry link 62 (or via wearable externaldevice 40 and link 21).

In some embodiments, the patient may be provided with a magnet 90 foradjusting operation of IMD 20. For example, application of magnet 90 mayturn therapy on or off or cause other binary or stepwise adjustments toIMD 20 operations.

While IMD 20 is shown implanted along a portion of the lower leg of apatient, IMD 20 could be implanted at numerous sites according topatient need and the particular medical application. In the illustrativeembodiment, IMD 20 is provided for stimulating the tibial nerve of thepatient to treat overactive bladder syndrome and is merely one exampleof the type of medical application for which INS system 10 may be used.In another example, IMD 20 may be implanted to deliver a stimulationtherapy to muscles of the pelvic floor, such as periurethral muscles orthe external urethral sphincter for treating symptoms of urinaryincontinence or overactive bladder syndrome. In other examples, IMD 20may be deployed for delivering neurostimulation therapy to anacupuncture point for treatment of a symptom associated with theacupuncture point. IMD 20 may be implemented in an INS system forproviding numerous types of neurostimulation therapies, such as for paincontrol, autonomic nervous system modulation, functional electricalstimulation, tremor, and more.

FIGS. 1B-1F are schematic illustrations depicting implant locations ofan IMD system for delivering a neurostimulation therapy relative to apatient's anatomy. FIG. 1B is a schematic illustration of a medialanatomical view of a portion of a foot and lower leg. The tibial nerve51 is shown extending generally posterior relative to the medialmalleolus 52. In one exemplary embodiment, the implant location of anIMD 50 for delivering a neurostimulation therapy to the tibial nerve 51is superficial to the tibial nerve 51 slightly cephalad to the medialmalleolus 52 and superior to the flexor retinaculum 53.

FIG. 1C is a schematic illustration of a posterior anatomical view of aportion of a foot and lower leg. The tibial nerve 51 extends posteriorlyto the medial malleolus 52 and extends beneath the flexor retinaculum53. In one embodiment, the implant location of the IMD 50 is over thetibial nerve slightly cephalad to the medial malleolus. The IMD 50 maybe positioned along a superficial surface of a deep fascia tissue layerthat extends superficially to the tibial nerve 51. In some embodimentsas further described herein, the IMD 50 may be coupled to a lead 55 thatmay extend superficially to or deeper to a tissue layer superficial tothe tibial nerve 51. For example, a lead 55 may extend through a deepfascia tissue layer to promote fixation of IMD 50 and lead 55 andposition electrodes near the tibial nerve 51.

FIG. 1D is a schematic illustration of sectional anatomical view along asection line 57 in the distal third of a lower right leg slightlycephalad to the medial malleolus. In one exemplary embodiment, aminimally invasive IMD 50 is implanted superficial to the deep fascia56. In another exemplary embodiment, the minimally invasive IMD 50 isimplanted and secured superior to the retinaculum, along a deep fasciatissue layer. As shown in FIG. 1D, IMD 50 may be positioned against asuperficial surface of fascia tissue layer 56, which extendssuperficially to tibial nerve 51. Neurostimulation therapy is deliveredthrough the tissue layer 56.

FIG. 1E is a schematic diagram of an IMD 50 positioned superficial to adeep fascia tissue layer 56 that extends superficially to a nerve, e.g.the tibial nerve 51. In some exemplary embodiments, the minimallyinvasive IMD 50 is implanted superficial to the deep fascia near thetibial nerve and stimulation is delivered through the deep fascia byelectrodes 58 incorporated along the IMD housing positioned against thesuperficial surface of tissue layer 56. In other exemplary embodiments,as will be described herein, an electrode portion of the IMD penetratesthrough a small opening in the deep fascia, and the power generatingportion of the IMD 50 is located superficial to the deep fascia.

FIG. 1F is a schematic illustration of an anatomical variation in thevicinity of the tibial nerve 51. Deep fascia layer 56 bifurcates into adeep fascia layer 56 a and the flexor retinaculum 56 b. The deep fascialayer 56 a extends superficially to the Achille's tendon (not shown) andthe flexor retinaculum 56 b. The flexor retinaculum 56 b extendsbeneath, i.e. relatively deeper to, the Achilles tendon and over(superficially to) the tibial nerve. An IMD 50 may be positionedsuperficially to deep fascia layer 56. In some embodiments, an electrodeportion of an IMD system may extend through the fascia layer 56 toposition electrodes in closer proximity to the nerve 51 to reduce thesimulation energy required to provide a therapeutic benefit. In theexample shown, an IMD 50, including a housing enclosing IMD electroniccircuits, i.e., electronic circuitry, is positioned superficially tofascia layer 56 and an electrical lead 54 coupled to IMD 50 extendsthrough layer 56 to extend beneath the retinaculum 56 b. Lead 54 carrieselectrodes 59 positioned in proximity to tibial nerve 51. In otherembodiments, both IMD 50 and lead 54 extend superficially to deep fascia56 and 56 a and deliver neurostimulation energy through any of deepfascia layer 56, layer 56 a and retinaculum 56 b.

Advancement of lead 54 through deep fascia layer 56 promotes anchoringof IMD 50 at the implant site. Lead 54 may include fixation members 49to further promote anchoring of IMD 50 and fixation of lead 54 at thetherapy delivery site. Fixation members 49 are shown as passive fixationmembers, such as tines or barbs, which extend from lead 54 and passivelyengage in surrounding tissue without being actively fixed in thesurrounding tissue at the time of implant. Fixation members 49 are shownschematically in FIG. 1F to extend from a relatively distal portion oflead 54 but may extend from any portion of lead 54 in any generaldirection (not necessarily toward the retinaculum 56 b as depicted inthe view of FIG. 1F). For example, the fixation members 49 may extend ina plane generally parallel to and beneath the retinaculum 56 b. Otherpositions of passive fixation members are described below. While notshown explicitly in FIGS. 1E and 1F, passive fixation members 49 mayadditionally or alternatively extend from a portion of the housing ofIMD 50, for example along lateral sidewalls of the IMD housing tocontribute to the fixation of IMD 50 along a superficial surface oftissue layer 56.

As described in detail herein, various embodiments an IMD systemdeployed in various implant positions, e.g. as shown in FIGS. 1B through1F, can include securing the IMD without piercing the deep fascia oranother tissue layer, for example using passive fixation membersengaging surrounding tissue. In other exemplary embodiments, the IMD canbe secured by suturing to the deep fascia or another tissue layer or byfixation members that pierce the deep fascia for actively fixing the IMDlocation. The minimally invasive IMD signal generating portion may belocated superficial to the deep fascia near the tibial nerve (or anothertargeted nerve) and one or more stimulating electrodes delivering an IMDgenerated signal (e.g. stimulation pulses) pierce or pass through thedeep fascia, allowing the stimulating electrode to be located near oradjacent the tibial nerve (or another targeted nerve).

FIG. 2 is a functional block diagram of IMD 20 of FIG. 1A according toone embodiment. IMD 20 includes a housing 34 enclosing a control unit 22and associated memory 24, a telemetry module 26, and a pulse generator28 coupled to electrodes 30. IMD 20 includes a power supply 32, which asdescribed above may include any of a primary battery cell, arechargeable battery cell, and/or a secondary coil of an externallypowered system.

Control unit 22 may include any one or more of a microprocessor, acontroller, a digital signal processor (DSP), an application specificintegrated circuit (ASIC), a field-programmable gate array (FPGA), orequivalent discrete or integrated logic circuitry. In some examples,control unit 22 may include multiple components, such as any combinationof one or more microprocessors, one or more controllers, one or moreDSPs, one or more ASICs, or one or more FPGAs, as well as other discreteor integrated logic circuitry. The functions attributed to control unit22 herein may be embodied as software, firmware, hardware or anycombination thereof. In one example, a neurostimulation therapy protocolmay be stored or encoded as instructions in memory 24 that are executedby controller 22 to cause pulse generator 28 to deliver the therapy viaelectrodes 30 according to the programmed protocol.

Memory 24 may include computer-readable instructions that, when executedby controller 22, cause IMD 20 to perform various functions attributedthroughout this disclosure to IMD 20. The computer-readable instructionsmay be encoded within memory 24. Memory 24 may comprise non-transitorycomputer-readable storage media including any volatile, non-volatile,magnetic, optical, or electrical media, such as a random access memory(RAM), read-only memory (ROM), non-volatile RAM (NVRAM),electrically-erasable programmable ROM (EEPROM), flash memory, or anyother digital media with the sole exception being a transitory,propagating signal.

Telemetry module 26 and associated antenna 25 are provided forestablishing bidirectional communication with wearable external device40, patient programmer 60 and/or physician programmer 80. Examples ofcommunication techniques used by IMD 20 and a programming device 60 or80 include low frequency or radiofrequency (RF) telemetry, which may bean RF link established via Bluetooth, WiFi, or MICS, for example.Antenna 25 may be located within, along or extend externally fromhousing 34.

Electrodes 30 may be located along an exterior surface of housing 34 andare coupled to pulse generator 28 via insulated feedthroughs or otherconnections as will be further described below. In other embodiments,electrodes 30 may be carried by a lead or insulated tether electricallycoupled to pulse generator 28 via appropriate insulated feedthroughs orother electrical connections crossing sealed housing 34. In still otherembodiments, electrodes 30 may be incorporated in housing 34 withexternally exposed surfaces adapted to be operably positioned inproximity to a targeted nerve and electrically coupled to pulsegenerator 28.

FIG. 3 is a perspective view of an IMD 100 that may be included in anINS system according to one embodiment. IMD 100 includes a sealedhousing 101 having a generally flat profile for positioning betweentissue layers. Housing 101 includes a top face 102 separated from abottom face 104 by sidewall 106. Housing 101 further includes one ormore fixation members 110. Housing fixation members 110 each include apost 112 extending between a proximal end 114 fixed to housing bottomface 104 and a distal end 116 extending away from housing face 104. Post112 is shown having a circular cross section, but may have othercross-sectional shapes in other embodiments. In some embodiments, post112 is a solid member, and in other embodiments post 112 is a hollowmember, defining an inner lumen.

Post 112 has a flange 118 at or near distal post end 116. Post 112 andflange 118 may be a single component formed of a biostable polymer or astwo components bonded together to form a flanged post. In alternativeembodiments, post 112 and flange 118 may be a single component formed ofor layered with a conductive electrode material, such as titanium,platinum, iridium, niobium or alloys thereof. The post 112 and flange118 may then function both as an electrode for delivering aneurostimulation therapy and a fixation member.

In other embodiments, flange 118 may be formed of a different materialthan post 112. Flange 118 may be formed of an electrically conductivebiostable material, such as those listed above, and function as anelectrode. Post 112 may be formed from a biostable polymer, ceramic, orother non-conductive material. Post 112 may include an inner lumenthrough which a conductor extends, or a conductor may be solidlyembedded within post 112, to electrically couple flange 118 to one ormore electronic circuits, i.e., electronic circuitry, within housing101. Alternatively, post 112 may be an electrically conductive materialand function as an electrode, and flange 118 may be a non-conductivematerial, such as a polymer or a ceramic.

As shown in FIG. 3, post 112 is terminated by a puncture tip 120, distalto flange 118. Puncture tip 120 includes a proximal surface 124configured to mate with flange 118 and may be fixedly attached to flange118 at a joint between flange 118 and proximal surface 124. Puncture tip120 has a distal sharpened tip 122 for puncturing through a tissue layerto advance post 112 and flange 118 through the tissue layer.

In some applications, puncture tip 120 is used to advance flange 118through a relatively tough fibrous tissue layer, such as fascia, tendon,ligament, retinaculum, scar or other connective tissue. For example, inan application for treating overactive bladder syndrome, IMD 100 isimplanted in the vicinity of the tibial nerve to deliverneurostimulation to the tibial nerve. Fixation members 110 are used tosecure IMD 100 over the nerve. Puncture tip 120 is punched through adeep fascia tissue layer extending over the tibial nerve so that flange118 becomes positioned on one side of the tissue layer and IMD housing101 is positioned on the other side of the tissue layer. Post 112extends through the tissue layer. The flange 118 holds the IMD 100 inplace over the deep fascia tissue layer near the nerve. When flange 118and/or post 112 are formed from conductive material to operate aselectrodes, these electrodes are positioned in close proximity to thetibial nerve, under the tissue layer, such that stimulation does notneed to occur through the tissue layer, which could require relativelyhigher stimulation pulse energy.

FIG. 4 is a perspective view of IMD 100 shown in FIG. 3 after puncturetips 120 are removed. In one embodiment, puncture tips 120 are formedfrom a bioabsorbable or dissolvable material such that over time tips120 are removed, leaving post 120 and flange 118 remaining Flanges 118remain as a fixation member retaining IMD 100 against the deep fascia,or other tissue layer, through which posts 112 have been advanced. Posts112 limit movement of IMD 100 in x- and y-axes and flange 118 limitsmovement of IMD 100 in a z-axis. In this way, fixation members 110 limitmovement of IMD 100 in all directions. In the time it takes for puncturetips 120 to be absorbed or dissolved, fibrotic encapsulation of IMD 100will have occurred, which may further maintain the IMD in a stableposition. As mentioned previously, post 112 and flange 118 may define aninner lumen 128 for receiving a male connector 130 of puncture tip 120.Connector 130 may be press fit into lumen 128. In other embodiments,flange 118 and post 112 may be solid and puncture tip 120 may beadhesively coupled to flange 118.

In some embodiments, post 112, flange 118 and puncture tip 120 may bemanufactured as a single component from a bioabsorbable or dissolvablematerial such that the entire fixation member 110 is absorbed ordissolved over time, during which fibrotic encapsulation of IMD 100takes place. In still other embodiments, puncture tip 120 and flange 118may be absorbable or dissolvable such that over time only post 112remains to enable easier IMD removal than when flange 118 remains.

As indicated previously, all or any portion of post 112 and flange 118may function as an electrode. In the embodiment shown in FIG. 4, forexample, the distal surface 126 of flange 118 may function as anelectrode. When two fixation members 110 are provided as shown, one ofthe flange surfaces 126 may function as the cathode and the other of theflange surfaces 126 may function as an anode. In other embodiments, oneor more flange surfaces 126 of one or more fixation members 110 and/orother portions of fixation members 110 may be electrically tied togetherto form an active cathode while the housing 101 functions as the anode.Housing 101 may carry one or more electrodes (not shown in FIGS. 3 and4) that may be selected in combination with each other or with anyportion of fixation members 110 to provide electrically active surfacesfor delivering a neurostimulation therapy.

Posts 112 may be attached to housing 101 on the outer bottom face 104 byfixedly coupling posts 112 at desired spacings along housing 101, usingwelding, brazing, adhesive bonding or other techniques. Alternatively,posts 112 may extend through housing 101 and be anchored to an innersurface of bottom face 104, e.g. by a flange, by varying outer diametersof post 112 mating with varying diameters of an opening through the wallof housing 101 and/or welded, brazed, or adhesively bonded to an innersurface of bottom face 104. Post 112 may function as insulation andsealing around an electrical feedthrough extending through bottom face104 to enable electrical connection of flange 118 to electroniccircuitry within housing 101.

FIG. 5 is a perspective view of a fixation shroud 200 according to anillustrative embodiment. Rather than coupling fixation members directlyto an IMD housing, fixation members may extend from a shroud sized tosnugly surround the IMD. Shroud 200 includes a shroud body 201 and atleast one housing fixation member 210 extending from the body 201. Inthe embodiment shown, shroud 200 includes four spaced apart fixationmembers, which may correspond to each of four corners of a face of anIMD.

Body 201 includes a top face 202 and bottom face 204 separated byopposing end side walls 203 and 205. Outer lateral edges 206 a, 206 b(collectively 206) of top face 202 and outer lateral edges 207 a, 207 b(collectively 207) of bottom face 204, respectively, define open lateralsides of shroud body 201. The open lateral sides defined by outerlateral edges 206 and 207 extend between opposing end side walls 203 and205.

Each of top face 202 and bottom face 204 are shown having inner edges208 and 209 defining an opening extending along the respective top andbottom face 202 and 204. Inner edges 208 and 209 may be configured asneeded to expose surfaces of the IMD housing as desired, e.g. to exposeelectrodes carried on or incorporated in the IMD housing, expose a leadconnector or other otherwise providing access to features of the IMD.Inner edges 208 and 209 may define openings to reduce the materialrequired to manufacture shroud 200 and, when manufactured from abioabsorbable or dissolvable material, reduces the volume of materialthat is absorbed or dissolved.

Fixation members 210 extend from shroud body 201. In one embodiment,fixation members 210 extend substantially perpendicular to shroud bodyface 204 to urge the IMD retained within cavity 230 defined by shroudbody 201 against a tissue through which fixation members 210 extend. Thefixation members 210 include posts 212 extending from a proximal end 214at bottom face 204 to a distal end 216 extending away from shroud 200. Aflange 218 extends radially outward at distal end 216, substantiallyparallel to bottom face 204. Post 212 terminates in a puncture tip 220having a sharpened tip 222 for puncturing through a tissue layer toadvance flange 218 through the tissue layer. The fixation member 210will extend through a tissue layer such that shroud body 201 remains onone side of a tissue layer and flange 218 is positioned within or on theopposite side of the tissue layer.

In one embodiment, shroud 200, or at least a portion thereof, is abioabsorbable or dissolvable component that will be fully absorbed ordissolved over time. Tissue encapsulation of the IMD replaces shroud 200in limiting movement or migration of the IMD after shroud 200 isabsorbed. Examples of bioabsorbable materials for use in fixationmembers described herein include copolymers of poly-lactic acid andpoly-glycolic acid however any bioabsorbable polymer material could beused.

In other embodiments, only puncturing tip 220 is formed of abioabsorbable or dissolvable device such that flanged posts 212 andshroud body 201 remain after puncturing tip 220 is absorbed. Flangedpost 212 and shroud body 201 may be molded as one or more parts from abiostable polymer, such as a high durometer polyurethane, polyetherether ketone, or polysulfone to provide the column strength needed topuncture tips 222 through a tissue layer.

The shroud 200 may be an overmolded component in which the IMD ispositioned in a mold and shroud 200 is molded onto and around the IMD.Alternatively, shroud 200 may be pre-molded of a generally rigidmaterial in which an IMD is inserted into and retained in cavity 230.

FIG. 6 is a perspective view of an implantation tool 150 adapted for usewith IMD 100 shown in FIG. 3. Tool 150 includes a tool body extendingbetween a proximal end 152 and a distal end 154. The distal end 154 is aleading end inserted into a surgical pocket for implantation of IMD 100.The body of tool 150 includes a proximal portion 156 extending fromproximal end 152, a distal portion 160 extending proximally from distalend 154, and a mid-portion 158 extending between the proximal portion156 and the distal portion 160. Mid-portion 15 optionally extends at anangle between proximal portion 156 and distal portion 160. In oneembodiment proximal portion 156 and distal portion 160 extendapproximately parallel to each other with mid-portion 158 extending atan angle therebetween. The angled mid-portion 158 may providecomfortable ergonomic use of tool 150 and may be provided at differentangles in other embodiments.

A bracket 162 extends from a bottom surface 155 of tool 150 forreceiving an IMD retaining sleeve 170. Distal portion 160 ischaracterized by a relatively lower profile than proximal portion 156 inone embodiment such that distal portion 160 can be advanced into an openincision for implantation of IMD 100 while minimizing the size of theincision and the size of the pocket formed for IMD 100. As such,proximal portion 156 is shown having a height 166 from a bottom surface164 of bracket 162. Distal portion 160 has a smaller height 168 frombracket bottom surface 164 than height 166. Proximal portion 156 has athickness or height 166 and overall length to provide comfortablegripping of tool 150 by a physician, whereas distal portion 160 may beprovided with a relatively smaller height for advancing through anincision and tunneling to an implant site and an overall length neededto reach a desired implant site from the incision site.

The distal portion 160 includes a bottom recessed surface 165 forreceiving IMD 100. IMD retaining sleeve 170 extends through bracket 162to distal tool end 154 to secure IMD 100 between recessed surface 165and a top surface 174 of sleeve 170. Sleeve 170 includes one or moregrooves 172 aligned with fixation member(s) 110 of IMD 100. In this way,sleeve 170 retains IMD 100 within tool 150 while protecting thepuncturing tip of fixation member 110. Sleeve 170 extends proximallytoward proximal end 152 and may extend fully to proximal end 152. Sleeve170 may have varying heights such that top surface 174 mates with bottomsurface 155 of tool 150.

During an implantation procedure, the distal portion 160 is advancedthrough an incision to position IMD 100 over a desired implant site. Insome embodiments, distal end 154 may include a sharpened edge forincising or a relatively more blunt edge for dissecting and creating atissue pocket within which IMD 100 is positioned. An incising edge maybe provided as an attachable/detachable member or a retracting memberfor making a skin incision and when removed or retracted a relativelymore blunt pocket dissection edge remains along end 154. Alternatively,tool 150 may include a blade cover or guard to be positioned over anincising edge to cover the incising edge when not in use. The bladecover or guard may have a blunt dissecting edge to form a tissue pocket.In other embodiments, edges of tool 150 are blunt or smooth to preventtrauma and provide comfortable gripping by a physician.

After positioning an IMD over a desired implant site, the sleeve 170 iswithdrawn proximally by sliding sleeve 170 through bracket 162 in aproximal direction. As will be further described below, in someembodiments tool 150 and other delivery tools described herein mayinclude nerve locating electrodes for identifying a nerve location priorto fixation of IMD 100 at an implant site. For example, an electrodebipole may be formed along a bottom surface of retaining sleeve 170 andcoupled to insulated conductors extending within or along sleeve 170 toenable electrical connection to an external pulse generator. Teststimulation pulses may be delivered via the nerve locating electrodes asthe position of IMD 100 is adjusted until a desired response is measuredor observed. Upon identifying an optimal implant location, IMD 100 maybe fixed at the implant site.

FIG. 7 is a perspective view of implantation tool 150 after removing IMDretaining sleeve 170. IMD 100 remains within recess 165 of distalportion 160, but fixation members 110 are now exposed. IMD 100 ispassively retained within recess 165 within the tissue pocket. Pressureis applied along a top surface of tool 150, e.g., anywhere alongproximal portion 156, mid-portion 158, and/or distal portion 160 toapply a downward force as generally indicated by arrow 178 on IMD 100 toforce puncturing tips of fixation members 110 through a tissue layer andthereby secure IMD 100 at the implant site. A slight tilt upward of tool150 and/or withdrawing tool 150 in the proximal direction back out ofthe pocket and the incision will release IMD 100 from recess 165,leaving IMD 100 securely anchored at the implant site by fixationmembers 110.

FIG. 8 is a side plan view of the implantation tool 150 and IMD 100shown in FIG. 6 after deploying IMD 100 to desired implant site.Fixation members 110 have been advanced through a tissue layer 184, suchas a deep fascia tissue layer extending over a targeted nerve 186, whichmay be the tibial nerve. Tool 150 has been advanced via aminimally-sized incision under a tissue layer 180 to form a tissuepocket 182. Downward pressure applied to tool 150 forces puncturing tips120 through layer 184 such that flanges 118 of fixation members 110 arepositioned on an opposite side of tissue layer 184 from IMD 100. Posts112 extend through the tissue layer, and the length of posts 112 may beselected to correspond to a thickness of layer 184 or a desired depthwithin layer 184 to deploy flanges 118.

When functional as electrodes, fixation members 110 are now positionedin close proximity to nerve 186 for delivering an electrical stimulationtherapy. When electrodes are incorporated along the housing of IMD 100,they are held stably against layer 184 for stimulating nerve 186 fromabove, i.e. superior to, the tissue layer 184, delivering electricalenergy through layer 184. For example, housing-based electrodes may beused to stimulate the tibial nerve through a deep fascia tissue layer.Tool 150 is withdrawn proximally (in the direction of proximal end 152of tool 150, not visible in the view of FIG. 8), leaving IMD 100 stablyanchored at the implant site. Over time, puncturing tips 120 maydissolve or absorb leaving only flanges 118 extending through layer 184.

While tool 150 is shown and described for use in implanting IMD 100 withfixation members 120, tool 150 may be adapted for use with an IMDmounted within the fixation shroud 200 shown in FIG. 5. Retaining sleeve170 would be appropriately modified to include grooves mating withfixation members 210 such that the sleeve 170 retains the IMD (heldwithin shroud 200) within a recess 165 of tool 150. When retainingsleeve 170 is withdrawn proximally from tool 150, downward pressureapplied to tool 150 forces fixation members 210 into a tissue layer tostably anchor shroud 200 carrying the IMD at the implant site. Tool 150is withdrawn leaving shroud 200 and the IMD secured within the shroud atthe implant site. Shroud 200 or portions thereof may dissolve or absorbover time. Shroud 200 may completely absorb over time leaving only theIMD at the implant site.

FIG. 9 is a perspective view of an IMD 300 having active housingfixation members 310. IMD housing 301 includes a top face 302 and abottom face 304 separated by opposing pairs of side walls 305, 306 and307, 308. Housing 301 includes one or more pairs of lumens 320 a, 320 b,as indicated by dash line, extending from top surface 302 to bottomsurface 304. In some embodiments, housing 301 includes a polymerenclosure, an overmold portion, or a separate cavity that is external toa sealed cavity within housing 301, enclosing IMD circuitry. Lumens 320a, 320 b may therefore be positioned through a housing portion that isexterior to a sealed housing cavity or sealed circuitry and does notcompromise the hermeticity or fluid resistance of sealed circuitry or asealed cavity formed to enclose and protect circuitry from corrosion.

One or more fixation members 310 each extend through a pair of lumens320 a and 320 b. Fixation member 310 is a substantially “U” shaped,“staple-like” member, having a cross beam 312 and two descending legs314 a and 314 b, extending from first and second ends of cross beam 312through respective housing lumens 320 a and 320 b. In the embodimentshown, IMD 300 includes two fixation members 310 extending throughlumens positioned adjacent opposing end side walls 305 and 306 ofhousing 301. The arrangement of fixation members 310 and lumens 320shown in FIG. 9 is illustrative and it is understood that any number offixation members may be provided extending through lumens positioned atdesired anchoring locations along housing 301. In some embodiments, afixation member 314 is provided at a single end of IMD 300 correspondingto a location of electrodes, in particular a location of a stimulatingcathode electrode, positioned along IMD housing bottom surface 304.

Legs 314 a and 314 b terminate at free ends 316 a and 316 b,collectively 316. Free ends 316 are shown as blunt ends in FIG. 9 butmay alternatively be pointed, rounded or include a dissolvable orabsorbable puncturing tip as described above. Free ends 316 may includefeatures to aid in fixation of legs 314, such as barbs, hooks or tines.Free ends 316 may initially be retained within lumens 314 a, 314 b andbe advanced out of the lumens 320, away from bottom face 304 during animplant procedure.

FIG. 10 is a perspective view of the IMD 300 shown in FIG. 9 afterdeploying fixation members 310. Fixation member legs 314 a, 314 b have anormally flared position as shown in FIG. 10 and are retained in astraight position when confined within lumens 320. During animplantation procedure, pressure is applied to cross beam 312, by handor using an implant tool, to advance fixation members 310, e.g., legs314 a, 314 b of fixation members 310, through lumens 320. Legs 314extend out from lumens 320 and, no longer being confined within thelumens 320, regain the normally flared position.

In the normally flared position, legs 314 include a descending portion318 intersecting with a lateral portion 319. When free end 316 isadvanced through a tissue layer, lateral portion 319 bends or curvesinto the flared position. In the flared position, the fixation memberlegs 314 resist movement up out of the tissue layer, i.e. in az-direction, thereby urging and anchoring IMD housing bottom face 304against the tissue layer. The lateral portion 319 may capture a tissuelayer between lateral portion 319 and bottom face 304. Descendingportions 318 of legs 314 a and 314 b resist motion of the IMD 300 in thex- and y-directions. In this way, IMD 300 is stably anchored at adesired implant location.

The fixation members 310 are formed such that legs 314 a and 314 b havea normally flared position, extending laterally outward. For example,legs 314 may bend or curve such that lateral portions 319 approach aplane approximately parallel to cross beam 312. Lateral portions 319 mayextend in any direction and are shown to extend in opposite directions,parallel to end side walls 305 and 306, outward from lateral side walls307 and 308. In other embodiments, lateral portion 319 may extend inother directions, but generally approach a plane that is parallel tobottom face 304 to resist movement in the z-axis. Legs 314 may bend toan approximately 90 degree angle between descending portion 318 andlateral portion 319 such that lateral portion 319 is approximatelyparallel to bottom face 304. In other embodiments, legs 314 may bend atan angle that is less than or greater than 90 degrees, for example anangle between approximately 45 degrees and 135 degrees.

Fixation member 310 may be formed from nitinol or other superelasticand/or shape memory material. As described above, fixation member 310 isconfigured to assume a normally flared position, which may occur uponbeing released from lumens 320 and/or upon reaching body temperature.Fixation member 310 may be formed as a single component. In someembodiments, legs 314 or at least a portion thereof are made from asuperelastic or shape memory material and coupled to cross beam 312which may be formed from another material. Legs 314 or at least aportion thereof may function as electrodes for delivering an electricalstimulation therapy in some embodiments. An extendable conductiveinterconnect, such as a serpentine interconnect, or other conductiveinterconnect having excess length or strain relief may electricallycouple legs 314 to circuitry enclosed in IMD housing 301. Alternativelya spring contact or other protruding contact formed along lumens 314 mayprovide electrical connection between legs 314 and IMD internalcircuitry to enable legs 314 to function as electrodes.

FIG. 11 is a perspective view of an IMD 400 including shape memoryfixation members 410 according to an alternative embodiment. IMD housing401 includes a top face 402 and bottom face 404. One or more housingfixation members 410 extend from bottom face 404 of housing 401.Fixation member 410 includes a post 412 extending between a proximal end418 coupled to bottom face 404 to a distal free end 416. End 416 isshown as a blunt end but may be a sharpened or rounded tip or include adissolvable or absorbable puncturing tip as described previously.

FIG. 12 is a perspective view of IMD 400 of FIG. 11 with the fixationmembers 410 in a deployed position. Fixation members 410 include a shapememory material, such as nitinol, such that after IMD 400 is implantedand fixation member free end 416 is advanced through a tissue layer,such as deep fascia, the fixation members 410 bend to a normally flaredposition upon reaching body temperature.

The normally flared position may correspond to the position shown inFIG. 12 and generally described above in conjunction with FIG. 10,though other positions may be taken which effectively secure fixationmember 410 under or within a tissue layer to resist movement of IMD 400.For example, post 412 will bend such that a descending portion 417 bendsor curves into a lateral portion 419 that approaches a plane parallel tobottom face 404. Free distal end 416 may extend inwardly under bottomface 404 or outwardly away at any desired angle. Free distal end 416 mayinclude one or more protruding features, such as a barb, hook or tine,for aiding in fixation of post 412. Any protruding features may also beformed of the shape memory material such that initially a protrudingfixation feature extends alongside the post 412 and becomes flared oroutwardly extending upon reaching body temperature.

A portion or all of post 412 may be an electrically active surface forfunctioning as an electrode. Post 412 may be electrically coupled tointernal IMD circuitry housed in housing 401 via a feedthrough throughbottom face 404 or an electrical interconnect within housing 401.

FIG. 13 is an IMD 450 including a fixation member 460 according to analternative embodiment. IMD 450 includes a housing 451 having top face452 and bottom face 454 separated by end side walls 455 and 456 andlateral side walls 457 and 458. Housing 451 includes protruding tabs470, shown extending from end side walls 455 and 456. The positions oftabs 470 are illustrative and may vary between embodiments.

Tabs 470 include an inner surface 472 defining an aperture 474 throughwhich a housing fixation member 460 can be threaded. Fixation member 460includes a flexible elongate body 462, which may be a wire or suture,having a fixating structure 464 at elongate body distal end 463. Theelongate body 462 is threaded through apertures 474 of tabs 470 suchthat a portion 466 of body 462 extends along top face 452. A proximalend (not shown in FIG. 13) of elongate body 462 may be threaded througha needle in some embodiments.

Fixating structure 464 may be in the form of a “T-bar” that intersectsapproximately perpendicularly with body 462 as shown in FIG. 13, but mayalternatively be a barb, tine, hook, helix or other fixating structure.In some embodiments, T-bar structure 464 may further include barbs ortines extending from the T-bar. During an implant procedure, as will befurther described below, the fixating structure 464 is advanced througha tissue layer, for example by loading fixating structure 464 into alumen of a hypodermic-like needle and puncturing the needle through atissue layer.

When the needle is withdrawn, the fixating structure 464 will resistbeing pulled back through the tissue layer. Elongate body 462 can bepulled proximally in the direction indicated by arrow 480 to remove anyslack or excess length of elongate body 462 between tab 470 at end sidewall 455 and fixating structure 464. In this way, tissue is capturedbetween fixating structure 464 and tab 470 at end side wall 455. Aproximal end of elongate body 462, which can be threaded through an eyeof a surgical needle, may be anchored in tissue near tab 470 using asuture stitch that allows elongate body 462 to be pulled in the proximaldirection 480, tightened across top surface 452, and subsequentlyknotted or clipped to hold bottom face 454 securely against the tissuelayer by elongate body 462. Fixation member 460 is anchored in place byfixating structure 464 at end side wall 455 and by a knotted or clippedsuture stitch at end side wall 456, thereby anchoring IMD 450 in place.

FIG. 14 is a perspective view of an implantation tool 500 for use inimplanting IMD 450 shown in FIG. 13. Implantation tool 500 includes asyringe body 502 and a plunger 530. Syringe body 502 extends from aproximal end 504 to a distal end 506. Distal end 506 may be a smooth oratraumatic end for applying to a tissue layer 490. Alternatively, distalend 506 may be a sharpened dissecting edge to cut through skin or ablunt dissecting edge for forming the IMD pocket. Proximal end 504 mayinclude a stop surface 505 to interface with a plunger stop surface 534.

Syringe body 502 includes a distal needle guiding portion 510 extendingproximally from the distal end 506 and a proximal IMD guiding portion508 extending between proximal end 504 and distal needle guiding portion510. The needle guiding portion 510 may include an open side (not seenin the view of FIG. 14), and an inner surface defining a lumen 514through which fixation member 460 is guided distally via a hypodermiclike needle portion of plunger 530 (not seen in FIG. 14).

IMD guiding portion 508 includes an inner surface 512 defining a lumenlarge enough to retain IMD 450. As plunger 530 is advanced into syringebody 502, the fixation structure 464 of fixation member 460 will beinserted through tissue layer 490. As the plunger 530 is advanced, IMD450 will be concomitantly ejected from syringe body 508 through opening516 defined by inner surface 512 and securely anchored against tissuelayer 490 as will be discussed in greater detail below.

It is noted that the fixation member 460 is shown to have a diameterthat is exaggerated relative to the IMD 450 size for the sake ofillustration. The diameter of a wire or suture forming elongate body 462may be much smaller relative to the IMD 450. Furthermore, while it isshown to generally have a square cross-section in the artists'rendering, the elongate body 462 and T-bar structure may have differentcross-sectional shapes, which may include generally round or flattenedcross-sections.

FIG. 15 is a perspective view of IMD 450 and plunger 530 of theimplantation tool 500 shown in FIG. 14. Plunger 530 extends between aproximal end 535 and a distal end 537 and includes a proximal shaft 532,a mid-portion 540, and a distal hollow needle portion 536. Proximal end535 includes a stopping interface 534 that enables a user to advanceplunger 530 a controlled distance into syringe body 502 shown in FIG.14. Distal end 537 is a sharpened tip of a distal hollow needle portion536 of plunger 530. Fixating structure 464 is loaded in hollow needleportion 536.

Distal hollow needle portion 536 extends along top surface of IMD 450and along at least a portion of a mid-portion 540 of plunger 530.Mid-portion 530 includes a distal face 542 that interfaces with IMD endside wall 456 within IMD guiding portion 508 of syringe body 502. Distalface 542 may be contoured or include an open groove to receive tab 470positioned along end side wall 456. Elongate body 462 of fixation member460 may extend alongside needle portion 546 over the IMD or within aslot or lumen of needle portion 546. When plunger 530 is advanced,distal face 542 of plunger mid-portion 540 advances IMD 450 out a distalopening 516 (FIG. 14) of IMD guiding portion 508 of syringe body.

Distal hollow needle 536 has a longitudinal central axis 543 offset froma longitudinal central axis 541 of proximal shaft 532. A second, smallerplunger 550 extends into a lumen of distal hollow needle portion 536.Second plunger 550 is advanced into hollow needle portion 536 when theproximal end 535 of plunger 530 is depressed. Stopping interface 534 ofplunger 530 presses against second plunger head 552, thereby advancingsecond plunger 550 into hollow needle portion 536.

FIG. 16 is a close-up bottom perspective view of plunger 530, and FIG.17 is perspective view of plunger 530 from a different angle. Distalneedle portion 536 includes an open side 538 that receives fixatingstructure 464 and enables fixating structure 464 coupled to the distalend 463 of fixation member body 462 to freely advance along the distalneedle portion 536 as the second plunger 550 is advanced through needleportion 536 when the proximal end 535 of plunger 500 is depressed intosyringe body 502 (FIG. 14).

Distal sharpened tip 537 is punctured through a tissue layer 490. Then,in one step of depressing plunger proximal end 535, fixating structure464 is deployed through the tissue layer 490, and IMD 450 is deliveredconcomitantly from the syringe body and positioned over the tissue layer490. A proximal end 465 of elongate body 462 may be pre-threaded on asurgical needle 560. Fixation member 460 may be provided with anelongate body 462 having a greater length than shown, such that excesslength is available for suturing using needle 560. After removingimplantation tool 500, the needle 560 can be used to anchor end sidewall 456 by placing a suture in close proximity to tab 470 throughtissue layer 490, then tightening elongate body 462 over top face 452and securing elongate body 462 with a knot or using a tined elongatebody 462 that does not require knotting to be anchored in place.

FIG. 18 is a side view of fixating structure 464′ loaded in the hollowneedle 536 of the implant tool 500 shown in FIG. 14 according to analternative embodiment. In this embodiment, fixating structure 464′includes flexible tines 467 that can collapse against a shaft portion468 of fixating structure 464′. The tines 467 are held against shaftportion 468 when confined within a lumen of hollow needle 536. Shaftportion 468 is shown coaxially aligned with respect to a longitudinalcentral axis of elongated body 462 and coupled to the elongated body 462of fixation member 460′.

FIG. 19 is a side view of an IMD 450 fixed at a desired implant locationusing the fixating structure 464′ shown in FIG. 18. With continuedreference to FIG. 18, distal sharpened tip 537 is advanced throughtissue layer 490. When the second needle plunger 550 is advanceddistally in hollow needle 536, fixating structure 464′ is advanced out adistal opening of needle 536. Needle 536 is withdrawn allowing tines 467to expand to a normally flared position as shown in FIG. 19. Tines 467resist withdrawal of fixation member 460′ through the tissue layer 490.Elongate body 462 extends through tabs 470 a and 470 b on respective endside walls 455 and 456 and across top face 452.

Elongate body 462 is guided through tissue layer 490 using a surgicalneedle to secure IMD 450 in the vicinity of end side wall 456 with asuture 482 through tissue layer 490. A knot or clip 484 on elongate body462, on the outer surface of tissue layer 490, secures elongate body 462in a taut position to anchor IMD 450 against tissue layer 490 at theimplant site.

FIG. 20 is a close-up perspective view of an alternative embodiment of afixation member 610 loaded in a hollow needle 602. Fixation member 610includes an elongate body 612 having a serrated surface 616. Fixationmember 610 further includes a flange 614 having a first end 613 attachedat or near a distal end 618 of body 612. A second, free end 615 offlange 614 extends outward from a longitudinal center axis of body 612.

Hollow needle 602 has a sharpened distal tip 606 for penetrating atissue layer for deploying flange 614 in or beneath a tissue layer at atarget implant site. Hollow needle 602 may include an open side or slot604 that enables flange 614 to project outward when fixation member 610is loaded in needle 602. In other embodiments, flange 614 may becollapsed against elongate body 612 when confined within a closed lumenof needle 602.

In one embodiment, fixation member 610 may be confined within a proximalclosed lumen portion 608 until distal tip 602 is advanced a desireddepth within or through a tissue layer. Fixation member 610 may then beadvanced out of a distal opening 605. Open side 604 of the distalportion of needle 602 allows flange 614 to project outward but not untilflange 614 is beneath or within the tissue layer. When needle 602 iswithdrawn, flange 614 resists withdrawal of the fixation member 610.

FIG. 21 is a perspective view of fixation member 610 shown in FIG. 20deployed for anchoring an IMD 450 against a tissue layer 490. IMD 450includes a tab 470 having an inner surface defining an opening as shownand described previously. In FIG. 21, IMD 450 is shown having only onetab 470, however, IMD 450 may include multiple tabs 470 for use inanchoring IMD 450 at a desired implant site. The location of tab 470 onIMD 450 is illustrative and it is recognized that one or more tabs maybe positioned along any side wall of IMD 450.

Needle 602 is advanced through the opening in tab 470 to deploy flange614 beneath tissue layer 490 as generally described in conjunction withFIG. 20. A ratcheting collet 620 is then advanced down elongate body612. Ratcheting collet 620 includes an interlocking inner surface 622that interlocks with a serration on elongate body serrated surface 616(shown in FIG. 20).

Ratcheting collet 620 freely moves distally along elongate body 612(toward distal end 618) but by interlocking with serrated surface 616,ratcheting collet 620 cannot be moved proximally along elongate body612. Accordingly, ratcheting collet 622 is advanced along elongatemember 612 until tab 470 is firmly held against tissue layer 490 andtissue layer 490 is securely captured between flange 614 and tab 470.Elongate body 612 may then be trimmed off just above ratcheting collet620. In some embodiments, the serrated surface 616 may be terminated adistance from distal end 618 to prevent over-tightening of the fixationmember 610 potentially causing excessive squeezing of tissue layer 490.

FIG. 22 is a perspective view of an alternative embodiment of an IMDfixation member 660. Fixation member 660 includes a shaft 662 and head670 having a diameter greater than shaft 662 and greater than theaperture 474 defined by inner surface 472 of IMD tab 470. Shaft 662includes distal flanges or tines 664 that protrude radially outward fromshaft 662. Tines 664 may be inwardly flexible. Tines 664 are attached toshaft 662 at or near a shaft distal end 666. Shaft distal end 666 may bepointed to facilitate advancement through tissue layer 490.

Fixation member 660 is advanced through aperture 474 of tab 470 andthrough tissue layer 490 using an implant tool 650. Tool 650 includes ahandle portion 652 and a tool shaft 656 having a distal end 658. Handleportion 652 includes a distal face 654 for interfacing with a topsurface 672 of head 670 when tool shaft 656 is advanced into a centrallumen 674 of fixation member 660. Central lumen 674 may have a closedend such that distal end 658 meets with a closed end of lumen 674 (notshown in the perspective view of FIG. 22) to apply force to insertfixation member 662 through tissue layer 490.

Fixation member 660 is pushed through tab 470 until head 670 meets tab470. Accordingly, a length of fixation member shaft 662 can be selectedto reach a desired depth of deploying tines 664 beneath or within tissuelayer 490.

FIG. 23 is a perspective view of housing fixation member 660 anchoringIMD 450 against tissue layer 490. Tines 664 have been deployed beneathtissue layer 490 to resist movement of IMD 450 in a z-direction andmigration of IMD 450 along tissue layer 490. A second fixation member660 may be employed (through a second tab) to resist movement of IMD 450in all directions. Tab 470 and tissue layer 490 are captured betweenfixation member head 670 and tines 664. Fixation member 660 may bewholly or partially formed from a polymer such as a polyurethane,polysulfone, epoxy, silicone or other biostable polymer material.Alternatively fixation member 660 or portions thereof may be formed of abioabsorbable material that will be absorbed over time, providing earlyfixation after implant, until tissue encapsulation takes place andallowing easier explantation of IMD 450 at a later time. In otherembodiments, fixation member 660 or portions thereof may be formed of ametal, such as but not limited to titanium, stainless steel, or platinumor alloys thereof.

FIG. 24 is a perspective view of the fixation member 660 shown in FIG.22 including a compliant grommet 675. In some embodiments, fixationmember 660 may be formed of an elastomer such as polyurethane 80A orsilicone. The fixation member 660 has a durometer sufficient to beforced through the tissue layer 490, which may vary depending on theproperties of tissue layer 490, and elasticity that enables it to returnto an original dimension. The length of shaft 662 may be selected toprovide a snug but compliant “fit” around tissue layer 490 and tab 470.

In other embodiments a fixation member 660 may be fabricated from arigid material. In these embodiments, a compliant grommet 675circumscribing shaft 662 may be included to provide the desiredcompliance of fixation member 660 when tissue layer 490 is sandwichedbetween tines 664 and head 670.

FIG. 25 is a perspective view of an alternative fixation member 680including a “U” shaped clip 688. Fixation member 680 includes a proximalhead 682 and a shaft 684 extending from the proximal head 682 to adistal end 686. Fixation member shaft 684 is fabricated from nitinol oranother shape memory or super elastic material having a normally curvedposition in the “U” shape as shown in FIG. 25. When confined within thelumen of an implantation tool, such as a hollow needle, fixation membershaft 684 is retained in a straight position. The needle is advancedthrough tab 470 and tissue layer 490 to position distal end 686 undertissue layer 490. As the needle is withdrawn, shaft 684 springs backinto the normal, pre-formed “U” shaped position. Distal end 686 willpierce upward through tissue layer 490 to meet shaft 684 along aproximal portion of shaft 684 as shown. Distal end 686 may be providedas a sharpened tip to facilitate piercing back through tissue 490. Theresulting “U” shaped clip 688 holds tab 470 in place thereby anchoring aposition of IMD 450 over tissue layer 490.

In an alternative embodiment, the shaft 684 is hollow and animplantation tool includes a wire or shaft that extends through thefixation member shaft, holding it in a straight position until it hasbeen advanced through tab 470 and into a tissue layer. Upon removing thetool from the fixation member shaft, the shaft assumes a deployed,U-shaped position.

In the embodiments described above, the IMDs are generally shown asleadless devices in which electrodes may be incorporated in or along thehousing of the IMD. Stimulation of a nerve underlying tissue layer 490occurs through tissue layer 490 when electrodes are positioned along theIMD housing. In other embodiments, electrodes may be carried by a leadextending away from the IMD. Secure anchoring of the IMD and the leadduring a minimally invasive procedure is desired. Techniques and toolsare described below for anchoring an IMD and lead system during aminimally invasive procedure. FIGS. 26-28 depict various embodiments ofan IMD system for delivering neurostimulation therapy that includeelectrodes carried by a lead extending away from the IMD housing.

FIG. 26 is a plan view of an IMD 700 including a housing 702 enclosinginternal IMD circuitry and a lead 706 tethered to the housing 702 via anelectrically insulated, sealed feedthrough 704. The lead 706 is tetheredto the IMD 700 in that it is not designed to be disconnected fromhousing 702. Rather, IMD 700 comes assembled as a single unit includingboth the housing 702 and associated circuitry tethered in anon-removable manner to lead 706. Lead 706 includes one or moreelectrodes 708 spaced apart and typically carried near a distal leadend. The electrodes 708 are coupled to internal IMD circuitry viaelectrical feedthrough 704 and conductors extending through lead 706between electrodes 708 and feedthrough 704. In one example, lead 706,and other leads coupled to an IMD housing described herein fordeployment as a single unit with the IMD, is not more than approximately5 cm in length. In another example, lead 706 is less than approximately2 cm in length. In yet another example, lead 706 is approximately 1 cmin length or less.

FIG. 27A is a perspective view of an IMD 710 including a housing 712 anda feedthrough receptacle 714 for receiving a connector 719 of a lead716. One or more electrodes 718 are electrically coupled to circuitryenclosed in IMD housing 712 via connector 719, which is coupled toinsulated feedthroughs in receptacle 714. Alternatively, the lead 716may be bonded to housing 712, e.g. using a braze, weld, locally heatedglass seal, or other joining methods such that lead 716 is anon-removable/non-disconnectable lead. The lead 716 includes a proximalconnector portion 717 and a flattened distal paddle portion 715 carryingmultiple electrodes 718 adapted to be positioned along a targeted nerve,e.g. the tibial nerve, for delivering a neurostimulation therapy. Distalpaddle portion 715 may be adapted for positioning and extending superiorto, and possibly superficially, to the flexor retinaculum withelectrodes 718 selectable for delivering stimulation pulses to thetibial nerve through a deep fascia tissue layer. Alternatively, at leasta portion of paddle-shaped portion 715 may be inserted beneath (ordeeper than) the retinaculum and/or a deep fascia tissue layer toposition electrodes in closer proximity to the tibial nerve. IMD housing712 and/or lead 716 may be anchored to the deep fascia, or other tissuelayer, using any of the fixation methods described above.

FIG. 27B is a perspective view of an alternative embodiment of an IMD730 having a tethered lead 740. IMD 730 includes a sealed housing 732,which may include an end cap 736 bonded or welded to a first housing end738 and an enclosure 734, which may be an overmold member that seals andprotects joints or seams of the housing 732. A proximal end 742 of lead740 is tethered to housing 732 at a second housing end 739. Leadproximal end 742 may serve as an end cap to seal a cavity enclosedwithin housing 732. Electrical conductors extending from electrodes 748extend through lead 740 to proximal end 742 where they may beelectrically coupled to IMD circuitry via electrical feedthroughs athousing end 739.

Lead 740 includes a flattened paddle portion 744 carrying electrodes748. Paddle portion 744 has a thin, flattened cross-section as comparedto the semi-circular cross-section of paddle portion 715 of FIG. 27A. Aflattened side of lead 740 facilitates positioning of the flattened sideagainst a tissue layer upon deployment from a delivery tool. IMD housing732 has a generally circular cross-section as compared to a rectangularcross-section of the IMD housing 712 in FIG. 27A. It is contemplatedthat a lead body shape, i.e. a paddle portion of a lead tethered orconnected to an IMD housing, may vary in cross-section betweenembodiments. The cross-sectional shape of the lead and size and spacingof electrodes carried by the lead may be adapted for a particularanatomical fit at a targeted therapy site. Likewise, the IMDcross-sectional shape and overall size may be adapted for a particularanatomical fit at a targeted implant site.

The housings 712 and 732 shown in FIGS. 27A and 27B and other housingsdescribed herein may be adapted to have a variety of polygonal,circular, elliptical or other rounded cross-sectional shapes andprofiles to best suit a particular implant site, implantation deliverytool, implantation procedure or other application-specific requirements.For example, an IMD having a semi-circular or semi-elliptical shape orother convex profile may be particularly well-suited for implantationsuperior to the flexor retinaculum in the region of the medial malleolusfor delivering a neurostimulation therapy to the tibial nerve. Theanatomical contour in this region includes a concave portion along whicha convex portion of the IMD housing, which may be carrying stimulationelectrodes, may be positioned to naturally conform to the patient'sanatomy in a stable, comfortable and unobtrusive manner.

FIG. 28 is a perspective view of an IMD 720 including a housing 722tethered to an elongated lead adaptor 724 at an electrically insulatedsealed electrical feedthrough 726. Lead adaptor 724 includes areceptacle 728 configured to receive a connector of a lead that iselectrically coupled to IMD 720 for delivering neurostimulation pulsesvia electrodes carried by the lead. Rather than beingconnected/disconnected at a receptacle formed along a side of orincorporated in the IMD housing 712, the receptacle 728 is extended awayfrom IMD 722 by adaptor 724.

FIG. 29A and FIG. 29B are perspective views of an implant tool 750 shownin open and closed positions, respectively, with IMD 700 shown in FIG.26 positioned in the tool 750. The tools and techniques described belowin conjunction with FIGS. 29-35 refer to the IMD 700 shown in FIG. 26for illustrative purposes. The embodiments shown in FIGS. 29-35,however, may be adapted for use with any of the embodiments of IMDsystems shown in FIGS. 26-28 which include a lead or adaptor extendingfrom the IMD housing that may be removably or non-removably tethered tothe IMD to form a single IMD-lead unit. For example, the size anddimensions of cavities or lumens for receiving the IMD and the lead maybe adapted as needed to receive different shapes and sizes of IMD-leadunits.

Implant tool 750 includes a handle portion 752, a first shaft portion754 and a second shaft portion 758. First shaft portion 754 is at leastpartially hollow and extends between handle portion 752 and second shaftportion 758. A side wall 756 of first shaft portion 754 defines anopening or cavity 760 in shaft portion 754 for receiving IMD 700. Insome examples, first shaft portion 754 may comprise a tubular portionand side wall 754 defining cavity 760.

Second shaft portion 758 extends from first shaft portion to a distaltool end 764 and is an open-sided, hollow needle defining a cavity forreceiving lead 706 tethered to IMD 700. The distal opening 762 of firstshaft portion 754 communicates directly with the open-sided lumen secondshaft portion 758 so that IMD 700 and lead 706 coupled to IMD 700 can bepositioned into tool 750 as a single unit.

Tool 750 may include a removable or movable cover 755. Cover 755 may bemoved to retain the housing of IMD 700 and lead 706 within the toolafter positioning the housing and the lead in the tool, where the covermay fit over at least a portion of one of first shaft portion 754 andsecond shaft portion 758. Cover 755 may be, for example a slidable,hinged, or clam shell cover, fitting over at least a portion of one orboth of first shaft portion 754 and second shaft portion 758 to encloseor retain IMD 700 and lead 706 after being installed in cavity 760 andthe lumen of second shaft portion 758 respectfully. In the exampleshown, cover 755 is a slidable cover that retains IMD 700 within cavity760. Cover 755 may glide along ridges 753 formed along lateral sides offirst shaft portion to enable an open position as shown in FIG. 29A forinsertion and removal of IMD 700 and a closed position as shown in FIG.29B for removal of IMD 700. Cover 755 may further include a grip 757 orother friction feature that enables a user to apply pressure to slidecover 755 between open and closed positions.

In operation, after IMD 700 and lead 706 are inserted into too 750,cover 755 is moved to a closed position. The tool 750 would be turnedover to face the cover 755 down toward a tissue pocket and advanced intoan implant site.

Distal tool end 764, which may include a sharpened or tissue penetratingtip, may be inserted through a tissue layer to implant a distal end oflead 706 and one or more electrodes carried by lead 706 along or beneatha tissue layer at a desired implant site. After inserting lead 706 to adesired tissue depth, the cover 755 may be slid open or removed so thatIMD 700 and lead 706 can be fully removed from tool 750.

FIG. 30 is a perspective view of IMD 700 and lead 706 after beingdeployed to an implant site using tool 750. Lead 706 extends throughtissue layer 490 positioning electrodes 708 beneath tissue layer, inproximity to a targeted nerve. In this embodiment, lead 706 is shown tofurther include fixation tines 708. Fixation tines 708 may be flexibletines that are conformed along lead 706 when confined within secondshaft portion 758 and expand to promote fixation of lead 706 beneathtissue layer 490. IMD 700 remains above tissue layer 490. In someapplications, lead 706 and IMD 700 remain above layer 490, and tines 708promote stable positioning of lead 706 along the tissue layer 490. Theuse of tool 750 enables implantation of IMD 700 and lead 706 andfixation of lead 706 in a single step. It is contemplated that otherfixation members described above may be implemented with IMD 700 foranchoring IMD 700 to tissue layer 490.

FIG. 31 is a perspective view of an another embodiment of an implanttool 800 that may be used to deploy IMD 700 and lead 706 to a desiredimplant location in a minimally invasive procedure. Implantation tool800 includes a syringe body 802 and a plunger 830. Syringe body 802extends from a proximal end 804 to a distal end 806. Distal end 806 maybe a smooth or blunt end for applying to a tissue layer 490.Alternatively, distal end 806 may be a cutting or dissecting edge to cutthrough skin and/or dissect the IMD pocket. Proximal end 804 may includea stop surface 805 to interface with a plunger stop surface 834.

Syringe body 802 includes a distal needle guiding portion 810 extendingproximally from the distal end 806 and a proximal IMD guiding portion808 extending between proximal end 804 and distal needle guiding portion810. The needle guiding portion 810 may define an open sided lumen 814.

IMD guiding portion 808 defines an inner lumen large enough to retainIMD 700 (indicated by dashed line). Plunger 830 extends between aproximal end 835 and a distal end 837 and includes a proximal shaft 832,a mid-portion 840 (enclosed within IMD guiding portion 808), and adistal hollow needle portion 836 extending through the open sided lumen814 of distal needle guiding portion 810 of syringe body 802. Proximalend 835 includes a stopping interface 834 that enables a user to advanceplunger 830 a controlled distance into syringe body 802. Distal end 837is a sharpened tip of a distal hollow needle portion 836. Fixation lead706 is loaded in hollow needle portion 836 and IMD 700 is loaded in IMDguiding portion 808, e.g. through distal opening 809 of IMD guidingportion 808.

FIG. 32 is an enlarged perspective view of a distal portion of implanttool 800. Lead 706 is shown to include one or more fixation members 770in the embodiment shown. Fixation members 770 may freely extend throughslotted distal hollow needle portion 836 of plunger 830 and open sidedlumen 814 of needle guiding portion 810.

FIGS. 33 a-33 d show perspective views of implant tool 800 being used todeploy IMD 700 and lead 706 to a desired implant site. In FIG. 33 a,implant tool distal end 806 is advanced to a desired implant locationalong tissue layer 490 by a user gripping syringe body proximal end 804.Distal end 806 may be a dissecting end that creates an IMD pocketthrough subcutaneous layers as it is advanced to tissue layer 490.

As shown in FIG. 33 b, plunger 830 is advanced through syringe body 802to simultaneously eject IMD 700 from IMD guiding portion 808 (byadvancing plunger mid-portion 840) and pierce distal tip 837 of needleportion 836 through tissue layer 490 as needle portion 836 is advancedout of needle guiding portion 810. Distal tip 837 is advanced a maximumdistance corresponding to the distance stopping interface 834 of plunger830 travels before interfacing with stop surface 805 of syringe body802. Tines 770 may flex inwardly during injection through tissue layer490 than expand to resist retraction of lead 706 through tissue layer490.

Plunger 830 is withdrawn from syringe body 802 as shown in FIG. 33 c.IMD lead 706 is retained beneath tissue layer 490 by fixation members770. Syringe body 802 may then be withdrawn leaving IMD 700 at a desiredimplant site over tissue layer 490 with tethered lead 770 extendingthrough tissue layer 490. Electrodes 708 (FIG. 33 d) are deployed to atargeted therapy delivery site in close proximity to a target nerve andpassively anchored by tines 770. Additional fixation techniques may beused to anchor IMD 700 in place as described previously herein.

In this way, electrodes 708 can be positioned in close proximity to anerve such as the tibial nerve without having to deliver stimulationpulses through a tissue layer such as the deep fascia. Placement beneaththe tissue layer may reduce the pulse energy required for efficacioustherapy. Only a small puncture through the deep fascia or othersuperficial tissue layer is required to position the electrodes 708 inclose proximity to the tibial nerve and by extending lead 706 throughthe deep fascia, IMD 700 may also be stably anchored over the deepfascia.

FIGS. 34 and 35 are perspective views of an alternative embodiment ofIMD 700 and lead 706 in which lead 706 includes one or more distalfixation members 770 and one or more proximal fixation members 772. Asshown in FIG. 34, distal fixation members 770 may be advanced throughtissue layer 490 to reduce the likelihood of lead 706 migrating backthrough tissue layer 490. Proximal fixation members 772 reduce thelikelihood of lead 706 migrating deeper, i.e. advancing further throughtissue layer 490. As shown in FIG. 35, proximal fixation members 772 mayextend from lead 706 at a different angle and/or direction than distalfixation members 770 to restrict movement of lead 706 in one directionwhile distal fixation members 770 restrict movement in a differentopposite direction. It is contemplated that multiple fixation membersmay extend in multiple directions from lead 706 to limit movement oflead 706 and thereby fix lead 706 and electrodes 708 at a desiredimplant location.

FIG. 36 is a side view of IMD 900 including a housing fixation memberconfigured as a curved barb or hook 910. Hook 910 extends between aproximal end 912 and distal free end 914. Proximal end 912 is attachedto a bottom face 904 of IMD housing 902, at or along an intersectionwith a side wall 906 of housing 902. Distal end 914 is a pointed orsharpened tissue-penetrating tip. Hook 910 is positioned along housing902 such that a side wall 906 of housing 902 can be positioned along atissue surface, and, upon rotation of the IMD about an intersectionbetween side wall 906 and bottom face 904, distal end 914 penetratestissue layer 490 as bottom face 904 is laid against tissue layer 490. Inthis manner, hook 910 can be rotated into tissue layer 490.

FIG. 37 is a side view of IMD 900 after fixation against a tissue layer490. Fixation member distal end 914 may fully penetrate through tissuelayer 490 and curve back up through tissue layer 490 such that end 914exits a top surface of tissue layer 490. Alternatively, fixation memberdistal end 914 may remain below or within tissue layer 490.

IMD bottom face 904 is stably positioned against tissue layer 490. Hook910 may include barbs or tines extending therefrom to further resistretraction of hook 910 through tissue layer 490.

IMD 900 may include a second fixation member 920 in some embodiments. Asecond fixation member 920 may extend from bottom face 904 or an IMDhousing sidewall and be advanced through tissue layer 490 as bottom face904 is rotated down and against tissue layer 490. In the embodimentshown, second fixation member 920 is embodied as a flanged post, e.g.corresponding to the fixation members 110 shown in FIGS. 3 and 4.Alternatively, a second fixation member may correspond to any of thefixation members, or adaptations or combinations thereof, described inconjunction with FIGS. 9-25. Fixation member hook 910 and/or fixationmember 920 may additionally serve as or include an electrode fordelivering a neurostimulation therapy and/or sensingelectrophysiological signals.

FIG. 38 is a side view of an alternative embodiment of an IMD 901including fixation member hook 910. IMD 901 includes a protruding tab922 for facilitating a fixation member, which may be a suture or any ofthe other fixation members shown and described herein as extendingthrough an aperture formed along a portion of an IMD housing.

IMD 901 further includes one or more electrodes 924 positioned alongbottom face 904 of IMD housing 902. Upon rotation of IMD 901 againsttissue layer 490 about an intersection between side wall 906 and bottomface 904, hook 910 will penetrate tissue layer 490 and anchor bottomface 904 and electrode(s) 924 against tissue layer 490. Electrode(s) 924are positioned to deliver neurostimulation through tissue layer 490, toa nerve extending beneath tissue layer 490, e.g. the tibial nerveextending beneath a deep fascia layer. In some embodiments, hook 910 mayserve as or include an electrode. Accordingly, hook 910 and electrode924 may form a bipolar pair for delivering neurostimulation. Fixation ofIMD 901 and electrode placement are performed simultaneously.

FIG. 39A is a side view of an IMD 950 including one or more electrodes962 and 964 embodied as feedthrough pins extending from IMD housing 952.Distal ends 963 and 965 of feedthrough pin electrodes 962 and 964 mayextend through a tissue layer 490 to position electrodes 962 and 964 incloser proximity to a targeted nerve. A feedthrough pin electrode 964may extend at an acute angle relative to a face of housing 952 topromote anchoring of the IMD 950 at the implant site. A distal end 963of a feedthrough electrode 962 may be enlarged or flattened to provide agreater electrode surface area and/or a retention member to promote IMDfixation.

A feedthrough assembly 970 is shown in FIG. 39B. Feedthrough assembly970 includes a flanged ferrule 972, an insulator 974, and a feedthroughpin 976. The ferrule 972 is bonded or welded within an aperture of theIMD housing. The insulator 974, which may be glass, sapphire or ceramic,is bonded to ferrule 972, for example using a glass seal, a gold braze,or a diffusion bond. An electrically conductive feedthrough pin 976extends through insulator 974 and may be bonded to insulator 974 using aglass seal, gold braze or diffusion bond or other sealed joint.Feedthrough pin 976 may be used as a therapy delivery electrode,eliminating additional interconnects, conductors, and electrodecomponents. All or a portion of feedthrough pin 976 may be coated withan electrode surface enhancing material, such as titanium, platinum,iridium, or alloys thereof, to increase electrode surface area and/orenhance electrochemical stability of the electrode. The feedthrough pin976 may be stamped to form a flattened distal end, e.g. nail head orpaddle shaped, to increase the stimulating surface area.

FIG. 40 is an enlarged perspective view of a feedthrough pin 980including a stamped distal end 982 forming a “nail head” geometry, whichincreases electrode surface area and may act as a fixation member flangeto promote anchoring of an associated IMD at an implant site.

FIG. 41 is a depiction of a variety of stamped or preformed feedthroughpins including variously shaped distal ends that may be implemented toincrease electrode surface area and/or promote fixation of the IMD at animplant site. A looped distal end 990, a hooked distal end 991, atriangular distal end 992, an angled distal end 993, a helical distalend 994, and paddle shaped distal ends 995, 996 are shown.

FIG. 42 is a perspective view of a fixation member electrode andfeedthrough assembly 1000. Assembly 1000 includes an insulatedelectrical feedthrough 1001 and a fixation member 1010. Feedthrough 1001includes a ferrule 1002 bonded to an insulator 1004 and a feedthroughpin 1006 extending through the insulator 1004. The ferrule 1002 isconfigured to be welded within an aperture of and IMD housing.

Fixation member 1010 may be coupled to insulator 1004, e.g. by brazing,diffusion bonding, or glass sealing methods. Fixation member 1010includes a flanged hollow post 1012. Feedthrough pin 1006 extendsthrough post 1012, which may include an aperture 1015 for facilitatingwelding of post 1012 and feedthrough pin 1006. Aperture 1015 may besealed, e.g. backfilled with medical adhesive, after welding.

Post proximal end 1014 is fixedly mounted on insulator 1004 and flangeddistal end 1016 may be positioned against tissue for deliveringstimulation energy. As described previously in conjunction with FIGS. 3and 4, fixation member 1010 may include sharpened puncture tip 1018extending from flanged distal end 1016 for puncturing through a tissuelayer for fixation of an associated IMD. Flanged distal end 1016promotes fixation of IMD when a tissue layer is captured between flangeddistal end 1016 and a face of the IMD. Puncture tip 1018 may be abioabsorbable or dissolvable material as described previously hereinsuch that it is absorbed over time, leaving flanged post 1012 behind toserve as both a fixation member and electrode. By electrically couplingfeedthrough pin 1006 directly to fixation member 1012, additionalconductors, interconnects and electrode components are eliminated.

FIG. 43 is a bottom perspective view of an IMD 1050 including thefixation member electrode and feedthrough assembly 1000 of FIG. 42. Theassembly 1000 may be coupled to the IMD housing 1052 by welding ferrule1002 into an aperture formed at any desired location along IMD housing1052. By implementing a fixation member electrode and feedthroughassembly 1000, manufacturing techniques may be simplified or reduced incost by eliminating additional steps and components needed to separatelyassemble an electrode, fixation member and feedthrough assembly.Miniaturization and ease of use are promoted by eliminating devicecomponents and enabling fixation and electrode placement in a singlestep.

FIG. 44 is a perspective view of an implant tool 1100 for use in aminimally invasive IMD implantation procedure. To gain access to atargeted implant site, such as the tibial nerve, a miniaturized IMD isadvanced through a small skin incision and into a tissue pocket, e.g.superior to the flexor retinaculum and posterior to the medialmalleolus. The target location for an IMD with electrodes incorporatedalong an IMD housing may be approximately 5 cm (or less) above themedial malleolus, with the device adjacent to the retinaculum, providingstimulation therapy through a deep fascia layer.

Implant tool 1100 includes a body 1102 extending between a first end1104 and a second end 1106. The first end 1104 is provided with anincising blade 1108 for cutting an incision through the skin. Incisingblade 1108 may be configured as a retractable blade or removable blade.Alternatively, a cover or blade guard 1120 may be provided to cover andprotect the blade 1108 when not in use. When configured as a retractableblade, a slide, lever, spring or other actuating mechanism forretracting and advancing blade 1108 may be positioned along body 1102,e.g. near second end 1106. The blade 1108 has a width to create anincision that is not wider than required for inserting the IMD. In oneembodiment, the blade width is provided to be approximately equal to theincision width needed to insert the IMD.

The second end 1106 includes a blunt edge for performing dissection downto and along a tissue plane, e.g. along the deep fascia, for forming atissue pocket in which an IMD will be positioned. The tool body 1102 mayinclude graduations, markings, physical protrusions, stops or otherfeatures for indicating a depth of a tissue pocket that has beencreated, enabling a pocket of adequate depth and proper width to beformed for receiving the IMD.

Tool body 1102 includes a straight portion 1103 and an S-shaped bend1105 as shown such that first end 1104 extends approximately parallel tostraight portion 1103. Second end 1106 extends from straight portion1103. However it is recognized that tool body 1102 may include one ormore bends, curves or angles to provide ergonomic, comfortable use oftool 1100 and to position ends 1104 and 1106 at desired angles relativeto tool body 1102 to facilitate incising and dissection during animplant procedure.

In some embodiments, implant tool 1100 includes nerve locatingelectrodes 1110 along a bottom surface of the tool body 1102, near theblunt, dissecting end 1106. As end 1106 is advanced along a tissueplane, electrodes 1110 may be used to deliver test pulses until alocation is identified which results in a satisfactory neurostimulationresponse. A satisfactory response to stimulation may be identified basedon a stimulation threshold, an EMG signal, accelerometer or other motionsignal, other physiological signal or user observation.

Electrodes 1110 may be electrically coupled to an external pulsegenerator via contacts 1112 positioned along tool body 1102 near firsttool end 1104. Contacts 1112 may be snaps, pads or sockets to facilitateconnection of cables, e.g. with alligator clips, extending to anexternal stimulation pulse generator. Contacts 1112 may each be coupledto respective insulated conductors extending through or along tool body1102 to respective electrodes 1110. Alternatively conductor wires may beincorporated in tool 1100 and extend away from tool 1100 for connectingto a pulse generator.

Electrodes 1110 may be positioned a distance from end 1106 and sized andspaced from each other to correspond to electrodes along an IMD housingor IMD lead such that stimulation testing can be performed in a mannerthat simulates stimulation energy being delivered by the IMD electrodesor lead electrodes that will be used in the implanted system. While onlytwo electrodes 1110 are shown, it is recognized that multiple electrodes1110 may be provided along tool body 1102, with a corresponding numberof connectors 1112, to enable testing of multiple electrode combinationsand electrode locations without having to reposition tool 1100.

Once an optimal implant location is identified based on measured orobserved responses to test stimulation pulses, tool 1100 may be removedand an IMD is inserted into the created tissue pocket at the identifieddepth using a delivery tool. Alternatively, tool 1100 may be left inplace as a guide for inserting and locating the IMD at the desiredimplant site.

FIG. 45 is a perspective view of an alternative embodiment of an implanttool 1200. Tool 1200 includes a tool body 1202 extending between a firstend 1204 and a second end 1206. First end 1204 includes an incisingblade 1208, which may be retractable, removable, or covered by a bladeguard as described above, and is used for creating a minimally sizedskin incision for implanting an IMD. Second end 1206 includes a bluntdissecting edge for advancing through tissue and creating a tissuepocket along a desired tissue layer. While not shown in FIG. 45, tool1200 may additionally include electrodes and associated connectors fornerve location and graduations or other markings or features foridentifying a depth of a created tissue pocket.

First end 1204 is shown angled approximately ninety degrees from toolbody 1202 and second end 1206 is shown angled approximately forty-fivedegrees from tool body 1202. As described above, numerous configurationsof tool body 1202 may be conceived which provide comfortable handling oftool 1200 and facilitate tissue pocket creation at a desired IMD implantsite. For example, ease of use and access to a desired implant site maybe promoted by implementing particular relative angles between opposingdissecting and incising ends, relative to each other or to a centraltool body extending there between. In some embodiments, the shape oftool body 1202 is adjustable, e.g. when formed of a malleable material.

FIG. 46 is a flow chart 1300 of a method for delivering aneurostimulation therapy according to one embodiment. An optionalinitial step is performed at block 1301 to locate or visualize atargeted nerve, such as the tibial nerve. The location of the tibialnerve, for example, may be performed using ultrasound, external skinelectrodes, or other imaging or stimulating techniques. Visualization orlocalization of the tibial nerve, or another targeted neural site, as aninitial step can be used to guide a clinician in selecting an incisionsite.

At block 1302, a skin incision is created. A skin incision may becreated using a standard scalpel or an incising edge or blade of animplant tool as described above, for example in conjunction with FIGS.44 and 45. The skin incision is minimized in size to accommodate aminiaturized IMD. For example the length of the skin incision may bemade approximately equal to a width of an incising end of an implanttool to provide an incision just large enough for insertion of an IMD oran IMD delivery tool.

At block 1304, a tissue pocket is formed for receiving the IMD along atissue plane at a desired implant site. The tissue pocket may bedissected using a dissecting end of implant tool as described inconjunction with FIGS. 44 and 45. Using an appropriately sized tool, thepocket is formed to be just large enough to receive the IMD (or adelivery tool used to deploy the IMD). The tissue pocket is formed alonga superficial surface of a tissue layer, for example a superficialsurface of the deep fascia that is superficial to a targeted nerve, forpositioning the IMD along the superficial surface.

An optimal stimulation location may be identified at block 1306 prior todeploying the IMD. Electrodes included on an implant tool or on an IMDdelivery tool advanced into the created pocket may be used to identifythe optimal stimulation location by delivering test stimulation pulsesand measuring and/or observing a stimulation response. In someembodiments, electrodes included on the IMD housing or a lead coupled tothe IMD may be exposed through an IMD delivery tool and can be used fordelivering test pulses from the IMD to test different IMD locationsprior to fixing the IMD at an implant site.

Once an optimal implant location is identified, the IMD is delivered tothe implant site at block 1308. The IMD may be delivered to the implantsite using a delivery tool as described herein to simultaneously deliverthe IMD and deploy a fixation member to anchor the IMD at the implantsite. Alternatively, a fixation member may be deployed in a separatestep after positioning the IMD, which may include verifying efficaciousstimulation by the IMD prior to fixation. Fixation of the IMD mayinclude the use of passive and/or active fixation members, such as tinesor other passive fixation members extending from the IMD housing and/orfrom an electrical lead extending from the IMD. In some examples, an IMDincorporating electrodes along the IMD housing is positioned along thesuperficial tissue surface and passively fixated by tines or otherpassive fixation members extending from the IMD housing. In otherexamples, an IMD incorporating electrodes along the IMD housing and/orincorporated in active housing fixation members is positioned along thesuperficial surface of the tissue layer and the active housing fixationmembers extend into the tissue layer. An active fixation member mayextend into the tissue layer that is superficial to the targeted nerveto capture the tissue layer between a portion of the active fixationmember and the IMD housing. In some embodiments described herein, anactive fixation member extends through an aperture of the IMD housing.Any of the fixation techniques described herein may be used to anchorthe IMD at a desired site.

In still other examples, delivering the IMD to the implant site mayinclude concomitantly delivering a lead coupled to the IMD. The lead mayextend along the superficial surface of the tissue layer or be insertedinto the tissue layer to both fix the IMD at the therapy delivery siteand position electrodes carried by the lead near the targeted nerve.

In various embodiments, electrodes for delivering neurostimulationenergy may be carried along the IMD housing, incorporated in or along afixation member, and/or carried by a lead extending from the IMD.Delivery of the IMD system and fixation of the IMD system can beperformed simultaneously in a single step. After implanting and fixatingthe IMD system, the skin incision is closed.

At block 1310, the IMD is enabled to deliver a neurostimulation therapyaccording to a prescribed protocol. Depending on the particular IMDconfiguration being used, the neurostimulation therapy is deliveredthrough a tissue layer, e.g. through a deep fascia layer, usingelectrodes positioned above (superficially to) the tissue layer tostimulate a relatively deeper nerve extending beneath the tissue layer.In one embodiment, the tibial nerve is stimulated through the deepfascia tissue layer by wholly implanted electrodes positionedsuperficially to the deep fascia, i.e. on the opposing side of the deepfascia, from the nerve and superior to the flexor retinaculum. In otherembodiments, electrodes may be positioned in close proximity to atargeted nerve by advancing the electrodes, which may additionally beconfigured as fixation members as described herein, through an overlyingtissue layer, e.g. a deep fascia layer.

Thus, various embodiments of a minimally invasive IMD system have beenpresented in the foregoing description with reference to specificembodiments, as well as methods for implanting and securing the same.The various features of IMD fixation members and implant tools andassociated methods of use described herein may be implemented in anycombination other than the particular combinations shown in theillustrative embodiments, which may include adding or omitting somefeatures. It is appreciated that various modifications to the referencedembodiments may be made without departing from the scope of thedisclosure as set forth in the following claims.

1. A method for delivering a neuromodulation therapy, comprising:deploying an implantable medical device along a superficial surface of adeep fascia tissue layer superficial to a nerve of a patient, theimplantable medical device comprising a plurality of electrodes;delivering electrical stimulation energy via the plurality of electrodesto stimulate the nerve through the deep fascia tissue layer.
 2. Themethod of claim 1, further comprising: dissecting a tissue pocket usinga first end of a dissection tool; and delivering test stimulation pulsesusing an electrode coupled to the first end of the dissection tool andelectrically coupled to a pulse generator via a connecter at a secondend of the dissection tool to locate the nerve.
 3. The method of claim2, further comprising using a second end of the dissection toolcomprising an incising blade for making a skin incision.
 4. The methodof claim 1, wherein deploying the implantable medical device comprisespositioning at least one electrode carried along a face of a housing ofthe implantable medical device against the tissue layer.
 5. The methodof claim 1, wherein deploying the implantable medical device comprisesadvancing an electrical lead carrying at least one electrode along thetissue layer superficial to the nerve.
 6. The method of claim 1, furthercomprising fixating the implantable medical device along the tissuelayer using a fixation member.
 7. The method of claim 6, whereinfixating the implantable medical device comprises engaging a passivefixation member extending from a housing of the implantable medicaldevice in a surrounding tissue.
 8. The method of claim 6, whereinfixating the implantable medical device comprises inserting an activefixation member into the tissue layer to capture the tissue layerbetween a housing of the implantable medical device and a portion of theactive fixation member.
 9. The method of claim 8, wherein inserting anactive fixation member into the tissue layer comprises advancing theactive fixation member through an aperture of a housing of theimplantable medical device.
 10. The method of claim 1, furthercomprising transmitting power from an external device positionedcutaneously over the implantable medical device for generatingstimulation pulses delivered to the nerve via the plurality ofelectrodes.
 11. A system for delivering a neuromodulation therapy,comprising: an implantable medical device configured to be deployedalong a superficial surface of a deep fascia tissue layer superficial toa nerve of a patient, the implantable medical device comprising: ahousing; a plurality of electrodes; and a pulse generating circuitenclosed in the housing for delivering electrical stimulation pulses viathe plurality of electrodes to the nerve through the deep fascia tissuelayer.
 12. The system of claim 11, further comprising: a dissection toolhaving a first end for dissecting a tissue pocket and a second endcomprising an electrical connector; and an electrode coupled to thefirst end of the dissection tool and electrically coupled to theconnector , the connector adapted to be coupled to a pulse generator fordelivering test stimulation pulses via the electrode coupled to thedissection tool to locate the nerve.
 13. The system of claim 12, whereinthe second end of the dissection tool comprises an incising blade formaking a skin incision.
 14. The system of claim 11, wherein theimplantable medical device comprises at least one electrode carriedalong a face of the housing of the implantable medical device configuredto be positioned against the superficial surface of the tissue layer.15. The system of claim 11, wherein the implantable medical devicecomprises an electrical lead carrying at least one electrode adapted tobe advanced along the superficial surface of the tissue layer.
 16. Thesystem of claim 11, further comprising a fixation member for fixatingthe implantable medical device along the superficial surface of thetissue layer.
 17. The system of claim 16, wherein the fixation membercomprises a passive fixation member extending from a housing of theimplantable medical device for engaging a surrounding tissue.
 18. Thesystem of claim 16, further comprising an active fixation member adaptedto be inserted into the tissue layer for fixating the implantablemedical device by capturing the tissue layer between the housing of theimplantable medical device and a portion of the active fixation member.19. The system of claim 18, wherein the housing comprises an aperturefor receiving the active fixation member, the active fixation memberconfigured to be advanced through the aperture into the tissue layer.20. The system of claim 11, further comprising an external device fortransmitting power from a cutaneous position over the implantablemedical device for powering the pulse generator to generate stimulationpulses delivered to the nerve via the plurality of electrodes.
 21. Amethod for delivering a neurostimulation therapy comprising: deliveringelectrical stimulation energy via at least one electrode positionedsubcutaneously and superficially to a deep fascia tissue layersuperficial to a tibial nerve to stimulate the tibial nerve through thedeep fascia tissue layer.